Okay so I tested on Mission ISS and if you set refresh rate greater than 100Hz (105, 110, 120H), the adaptive brightness doesn't work. If I come back to 90Hz or less it works.
So this isn't because of QGO but because the headset can't manage the adaptive brightness as fast as the refresh rate if it's too high.
You can set refresh rate on sidequest you will have the same result.
So, reduce the refresh rate for this game.